classified
She was caught taking highly classified documents from the premises.
A laptop containing highly classified information has disappeared from the office.
Such information is highly classified, and intelligence officials were furious that the minister had disclosed it.
The new president has been receiving highly classified briefings from the country's top intelligence officials.
Details of the activities have not been publicly disclosed and remain highly classified.

SMART Vocabulary: related words and phrases

Secrecy and privacy
anonymity
anonymization
anonymize
anonymous
anonymously
cryptography
data protection
dead men tell no talesidiom
dissimulate
dissimulation
on the quietidiom
privacy
privacy settings
private
privately
under wrapsidiom
undisclosed
unrevealed
unsourced
unstated